i) Technical Field of the Invention
This invention relates to a state monitoring technique for apparatuses connected with a network.
ii) Description of the Related Art
Conventionally, there has been a technique for monitoring states of apparatuses on a network.
FIG. 13 is a block diagram illustrating a brief outline of communications exchanged in a conventional network system.
As shown in FIG. 13, this network system comprises a directory service 110 as a monitoring apparatus for monitoring states of apparatuses connected with the network. This directory service 110 manages information regarding a plurality of apparatuses (printer 120, in FIG. 13) to be managed, which are connected with the network, based on information received from the apparatuses, and supplies the managed information at the request of the other apparatuses. Thereby, when a user of a personal computer (hereinafter, referred to as client PC) 130 utilizing the directory service 110 intends to print printing data generated in the client PC 130 on a printer on the network, for example, it is possible for the user to search for a printer currently available from the information managed by the directory service 110 and to transmit the printing data to the searched printer 120.
This network system further comprises a personal computer (hereinafter, referred to as apparatus management PC) 140, as another monitoring apparatus different from the aforementioned directory service 110, having a function to manage specific apparatuses on the network. This apparatus management PC 140 manages information regarding a plurality of specific apparatuses (printer 120, in FIG. 13), which are connected with the network, based on information received from the specific apparatuses, and displays the managed information on a not shown display of the apparatus management PC 140 at the request of a user of the apparatus management PC 140.
The information which such monitoring apparatuses receive from the monitored apparatuses on the network includes information which the apparatus voluntarily transmits and information which the apparatus returns at the request from the monitoring apparatuses. At all events, the monitoring apparatuses can receive the information only when the monitored apparatuses are alive on the network. In other words, if the monitored apparatuses are disconnected from the network by being powered off or the like, it is natural that the information from the monitored apparatuses cannot be received.
In case of a personal computer which is powered off after shutdown operation, it can voluntarily transmit the information that it is going to be disconnected from the network when the shutdown operation is performed. On the other hand, in case of a general printer which is powered off all of a sudden without such shutdown operation, for example, it cannot voluntarily transmit the information that it is going to be disconnected from the network.
For the above reason, in the aforementioned conventional network system (FIG. 13), the printer 120 is designed to periodically transmit the information to the monitoring apparatuses, that is, to the directory service 110 and the apparatus management PC 140, respectively. Each of the monitoring apparatuses detects the disconnection of the monitored apparatus from the network at the time when it determines that the information to be received at regular intervals has not been received.
As described in the above, in this type of the network system, the information is transmitted from the monitored apparatus like a printer to the monitoring apparatuses per a predetermined timing. The more frequently the information is transmitted, the heavier the network traffic becomes. Therefore, the transmission frequency of the information is controlled to be low.
However, if the transmission frequency is set to be low, it may take long, from when the monitored apparatus like the printer is in fact powered off, for the monitoring apparatuses to detect the disconnection of the monitored apparatus from the network. If the detection takes long as such, there may be cases in which the monitored apparatus determined to be alive on the network by the monitoring apparatuses is no longer alive on the network. Thus, reliability of the information managed by the monitoring apparatuses is threatened.